CN111785504A - Near-net-shape preparation method of rare earth permanent magnet - Google Patents
Near-net-shape preparation method of rare earth permanent magnet Download PDFInfo
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- CN111785504A CN111785504A CN202010663484.3A CN202010663484A CN111785504A CN 111785504 A CN111785504 A CN 111785504A CN 202010663484 A CN202010663484 A CN 202010663484A CN 111785504 A CN111785504 A CN 111785504A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0266—Moulding; Pressing
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
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- Manufacturing Cores, Coils, And Magnets (AREA)
Abstract
The invention relates to a preparation method of a rare earth permanent magnet, in particular to a near-net-shape preparation method of the rare earth permanent magnet. Solves the problems of large deformation of sintered rare earth permanent magnets and high cracking rate of ring and sheet products in the prior art. A near-net-shape preparation method of a rare earth permanent magnet is realized by the following steps: 1) smelting rare earth alloy; 2) crushing the alloy; 3) adding the magnetic powder into a movable die cavity, and carrying out low-pressure magnetic field molding; 4) putting the mould containing the green body into a vacuum degreasing furnace for degreasing, removing gas adsorbed by the green body, volatilizing organic additives in the green body and residual hydrogen in the crushing process, and heating to the temperature required by hot pressing; 5) and (4) carrying out hot pressing on the degreased green body to enable the density of the workpiece to reach the density required by the finished permanent magnet, cooling, demoulding, and carrying out secondary aging treatment to obtain the finished permanent magnet. The section size is the same as the die, and the near-net forming without processing or with less processing is realized. The preparation method is suitable for permanent magnets of various shapes, and is particularly suitable for ring and sheet products.
Description
Technical Field
The invention relates to a preparation method of a rare earth permanent magnet, in particular to a near-net-shape preparation method of the rare earth permanent magnet.
Background
In the prior art, rare earth permanent magnets are obtained through a sintering process. The volume shrinkage rate of the rare earth permanent magnet exceeds 40% in the sintering process, and the shrinkage rate in the magnetic field direction is nearly twice as large as that of a non-magnetic field method, so that the shrinkage deformation is large, more grinding amount is reserved, the grinding is time-consuming and labor-consuming, and the material yield is low. Ring and tile shapes, and high breakage rate during grinding. The cracking rate of the multi-pole magnetic ring and the radiation magnetic ring is particularly high.
Disclosure of Invention
The invention solves the problems of large shrinkage deformation amount, large grinding amount and high ring product cracking rate of the rare earth permanent magnet in the prior art, and provides a preparation method of the rare earth permanent magnet to overcome the problems.
The invention is realized by adopting the following technical scheme: a near-net-shape preparation method of a rare earth permanent magnet is realized by the following steps:
1) smelting rare earth alloy;
2) crushing the alloy;
3) filling the magnetic powder into a movable mould, placing the movable mould into a magnetic field press for low-pressure magnetic field forming to enable the density to reach 3.2-3.5g/cm < 3 >, and then taking out the magnetic powder together with the mould;
4) putting the green bodies and the molds into a vacuum degreasing furnace together in batches, removing gas adsorbed by the green bodies, volatilizing organic additives in the green bodies and hydrogen remained in the hydrogen crushing process; the degreasing process can be easily determined by a limited number of tests according to the volume size of the green body, the amount and kind of the organic additives, and the amount of residual hydrogen. The carbon content is less than 1000 ppm. The former stage temperature is used for degreasing, and the latter stage temperature is used for temperature preparation of dehydrogenation and hot pressing.
5) Hot pressing after degreasing
After the vacuum degreasing is finished, cooling is not carried out, argon is filled, the pressure of the hot pressing chamber is balanced, the pressure is the same as the atmospheric pressure or slightly positive pressure, and the oxygen concentration is ensured to be lower than 100 ppm. The mould and the green body are directly placed into a hot pressing machine. Therefore, the energy consumption is low and the efficiency is high. Because the temperature is high, the manual operation is not easy, and special automatic equipment integrating degreasing and hot pressing is needed.
Because the quantity of the moulds used for turnover is large, the moulds are made of high-density graphite materials with low price, and the strength and the service life of the high-density graphite materials are much lower than those of hard alloy, but the high-density graphite materials can meet the general production requirements.
The green body is not demoulded and enters a degreasing furnace together with the die for degreasing, mainly because the thin-wall green body has low high-temperature strength, the ring green body is grabbed by a mechanical claw, the breakage rate is high, and the ring green body is difficult to align to a die cavity.
For thick-walled or solid products, the green body can also be placed directly into a degreasing furnace after demolding, rather than into a mold. Then the mold is held by a mechanical claw and put into a mold cavity to carry out hot pressing.
Range of hot pressing temperature: when the temperature is lower than 550 ℃, the pressure is higher, and the green body is difficult to reach the density required by the finished permanent magnet (7.5-7.6 g/cm for neodymium iron boron)3) However, temperatures above 1000 ℃ are advantageous for increasing the hot pressing density (the pressure is inversely proportional to the temperature, i.e., the higher the temperature, the lower the pressure required to achieve the finished permanent magnet density). However, if the temperature is too high, the grains of the rare earth permanent magnet material will grow up, which will affect the performance of the permanent magnet. Therefore, in the case where the density of the finished permanent magnet is known and the common knowledge in the art is known, the temperature and pressure required for hot pressing in this step can be easily obtained by limited experiments. Therefore, the temperature and the pressure are between 550 and 1000 ℃, preferably between 760 and 950 DEG C
The invention provides a novel preparation process of a rare earth permanent magnet, which uses a movable mould to carry out low-density magnetic field forming. The permanent magnet with the required finished product density is obtained by vacuum degreasing and hot pressing, so that the problems of large sintering deformation and high ring product cracking rate in the prior art are solved, and the cost is reduced; meanwhile, the hot-pressed green body has standard shape and high size precision, the grinding process can be omitted, and the outer surface of the green body is slightly oxidized in the degreasing and hot-pressing processes to form a compact oxide layer which is a natural protective layer and can not be electroplated under many conditions, so that the preparation process is simplified; because of the low cold pressing density, the vacuum degreasing is easy to carry out, and the speed block is removed.
The hot pressing temperature is lower than the sintering temperature, and the crystal grains are not easy to grow. The method is particularly beneficial to adopting a double-alloy method, the heavy rare earth element only permeates into the surface layer of the main phase to form a core-shell structure, and a double-high product with high coercivity and high remanence is obtained. The result is that heavy rare earth permeates on the surface, but the manufacturability is far better than that of heavy rare earth diffused on the surface. The preparation method is suitable for permanent magnets of various shapes, and is particularly suitable for multi-pole magnetic rings, radiation magnetic rings, tile shapes and sheets.
Drawings
FIG. 1 is an electron micrograph of the powder after jet milling;
FIG. 2 is an electron micrograph of neodymium iron boron permanent magnet after 900 deg.C aging.
Detailed Description
A near-net-shape preparation method of a rare earth permanent magnet is realized by the following steps:
1) smelting rare earth alloy;
2) crushing the alloy;
3) filling magnetic powder into the movable mould, vibrating, beating or low-pressure forming to make the density reach 3.0-3.5g/cm3, and then carrying out magnetic field orientation with the mould;
4) and (3) carrying out vacuum pre-sintering on the green body, only removing gas adsorbed by the green body, volatilizing organic additives in the green body and hydrogen remained in the hydrogen crushing process, and avoiding shrinkage of the green body. In the specific implementation, the vacuum degreasing temperature is preferably 300-500 ℃ and 650-950 ℃. (for example, 400 ℃ for 2 hours and 900 ℃ for 3 hours may be selected). In the temperature rise process of vacuum degreasing, the temperature rise speed is controlled to be 5-10 ℃/min. The heat preservation time interval is set to ensure that the heating is uniform, the air is fully discharged, and the carbon adding amount is reduced. The latter stage is mainly to remove the residual hydrogen and raise the temperature above the temperature of the hot press forming.
5) And further carrying out hot pressing on the degreased green body and the mould to enable the density of the green body to reach the density required by the permanent magnet.
After the vacuum degreasing is finished, cooling is not carried out, argon is filled, the pressure of the hot pressing chamber is balanced, the pressure is the same as the atmospheric pressure or slightly positive pressure, and the oxygen concentration is ensured to be lower than 100 ppm. Directly placing the mold and the green body into a hot-pressing machine, and if the temperature is lower than the hot-pressing temperature, performing medium-frequency induction heating; if the temperature is proper, hot pressing is directly carried out. Therefore, the energy consumption is low and the efficiency is high. Because the temperature is higher, the manual operation is difficult, and corresponding automatic equipment is needed.
And carrying out hot pressing on the green body in the die to ensure that the density of the green body reaches the density required by the finished permanent magnet, and obtaining the finished permanent magnet after aging. In specific implementation, preferably, the mold and the green body therein are heated to 650-; at this temperature, the grains hardly grow and maintain the size after the jet milling. The coercive force is improved compared with the common sintering, and the remanence is not reduced. The mold and the green body therein are heated to a desired temperature, kept warm for 0.3-10 minutes (for example, 0.3 minute, 0.5 minute, 0.8 minute, 1 minute, 3 minutes, 5 minutes, 6 minutes, 8 minutes, 9 minutes, 10 minutes are selected), pressurized to a desired pressure, and then kept for 0.3-10 minutes (for example, 0.3 minute, 0.5 minute, 0.8 minute, 1 minute, 3 minutes, 5 minutes, 6 minutes, 8 minutes, 9 minutes, 10 minutes are selected) to ensure the heat and pressure are kept constant. The longer dwell time is beneficial to the increase of density and the improvement of density uniformity, but too long will inevitably affect the production efficiency, and further too long will possibly cause the crystal grains of the magnetic material to grow up and affect the magnetic performance.
And performing 900 ℃ aging treatment on the hot-pressed workpiece, passivating the sharp corners of the particles, combining small particles, uniformly distributing a neodymium-rich phase, and completely and clearly preparing a grain boundary, and performing 490-520 ℃ low-temperature aging to further improve the coercivity. And obtaining the permanent magnet product.
The mold material may be selected from graphite, heat-resistant mold steel, cemented carbide, ceramics, etc. according to temperature, pressure, batch, etc. If necessary, the die cavity is sprayed with high-temperature lubricant such as molybdenum disulfide and the like.
Example 1
Vacuum melting, preparing 48H quick-setting tablets, and quickly setting and spinning to obtain quick-setting sheets with the thickness of 0.25-0.35 mm.
The rapidly solidified flakes HD were coarsely crushed according to a conventional method. 800 PPM residual hydrogen.
Milling with a jet mill to an average particle size of 3.2 microns. The total amount of the antioxidant and the lubricant is 0.3 percent. Wherein the methyl caproate is wetted by 15 percent, the isomeric dodecyl alkane is wetted by 20 percent, the zinc stearate is wetted by 2 percent, the coupling agent is wetted by 5 percent, and the rest is hydrocarbon diluent.
The graphite mold has the film size of 80 mm in outer diameter, 30mm in inner diameter and 100mm in mold cavity depth. The oriented core rod material is bearing steel. The hot pressing core rod material is graphite.
Adding 75g of magnetic powder into a graphite mold; then the powder is placed on a vibration platform to be compacted, and the powder filling density is about 2.2g/cm3. Placing on a rotary magnetic field platform, applying a magnetic field with a magnetic field of 1.2, a pressure of 5MPa and a density of 3.5g/cm for pressing3。
Taking out the bearing steel core rod, replacing the graphite core rod, putting the mold containing the green body and the core rod into a vacuum degreasing furnace together, keeping the vacuum degree at 0.01Pa, heating to 400 ℃ at the speed of 5 ℃/min, and keeping the temperature for 120 min; then the temperature is raised to 900 ℃ according to the speed of 5 ℃/min, and the temperature is preserved for 60 min. Then, argon gas was introduced. When the pressure is 0, opening a gate valve between the hot pressing cabin and pushing the hot pressing cabin.
The hot ballast was previously replaced by argon to bring the oxygen concentration below 50 ppm.
Placing the mold and the green body on the mold of a press by a mechanical claw, pressing at 50MPa, and maintaining the pressure for 60S to obtain a product with a density of 7.6g/cm3. Cooling to 80 ℃, and discharging. And carrying out 900-degree aging for 6 hours and then carrying out 500-degree aging for 5 hours to obtain the radiation magnetic ring with 48H performance. The direct dimension is not changed, and only the height direction is reduced by half.
Example 2
0.6% of Tb (80%) -Cu (20%) alloy powder was added during compounding. The rest is the same as example 1. A high remanence, high coercivity magnet of 46EH was obtained.
FIG. 1 is an electron micrograph of the powder after jet milling at 10000 times. The largest particle is 7-8 microns.
FIG. 2 is an electron micrograph of the permanent magnet after aging at 900 ℃ with the largest particles also being 7-8 microns.
Because the hot pressing temperature is low, the time is short, and the crystal grains are hardly grown.
This scheme can also be used to the manufacturing of class metal permanent-magnet such as samarium cobalt, alnico. It can also be used for hot-press forming of tiles, fans, wafers, square sheets, squares or irregular blocks.
The above examples are merely representative of preferred embodiments of the present invention, and the description thereof is more specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, various changes, modifications and substitutions can be made without departing from the spirit of the present invention, and these are all within the scope of the present invention.
Claims (8)
1. The near-net-shape preparation method of the rare earth permanent magnet is characterized by comprising the following steps of:
1) smelting rare earth alloy;
2) crushing the alloy;
3) filling the magnetic powder into a movable mould, forming the magnetic powder by a low-pressure magnetic field to ensure that the density reaches 40-50% of the density of a product, and then taking the magnetic powder out together with the mould;
4) without demolding, the green body and the mold are subjected to a vacuum degreasing furnace together, gas adsorbed by the powder is removed, organic additives in the green body and hydrogen remained in the HD process are volatilized, and the temperature is raised to the hot-pressing temperature;
5) after degreasing, pushing a hot pressing cabin, putting the die and the green body on a die frame of a pressing machine, and performing hot pressing to ensure that the density of the green body reaches the density required by the permanent magnet; cooling and discharging;
6) and (5) performing aging treatment to obtain a final product.
2. The near-net shape manufacturing method of a rare earth permanent magnet according to claim 1, wherein the die material is graphite, cemented carbide, or heat-resistant steel material.
3. The method as claimed in claim 1, wherein the degreasing temperature in step 4) is selected from the range of 300 ℃ and 750 ℃ to 950 ℃, the secondary degreasing is performed, and the total degreasing time is selected from the range of 3 to 6 hours.
4. The near-net shape preparation method of rare earth permanent magnet according to claim 1, wherein in step 5), after degreasing, intermediate frequency induction heating can be used for supplementary heating, and the temperature is kept for 0.3-2 minutes to reach the temperature required by the heating process.
5. The near-net-shape production method of a rare earth permanent magnet according to claim 1, wherein the aging treatment includes secondary aging treatments of 900 ℃ and 500 ℃.
6. The near-net shape preparation method of a rare earth permanent magnet as claimed in claim 1, wherein the powder containing one or two alloys of terbium, dysprosium, holmium is added to the pulverized powder in an amount of 0.1-5%.
7. The near-net-shape production method of a rare earth permanent magnet according to claim 5, wherein the time of 900 ℃ aging treatment is 3 to 10 hours.
8. The near-net shape manufacturing method of a rare earth permanent magnet according to claim 1, wherein in step 4), 5) the vacuum degreasing furnace and the hot pressing device are connected by a sealed channel, and the oxygen content is less than 100 Pppm.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104892004A (en) * | 2015-05-18 | 2015-09-09 | 山东理工大学 | Preparation process of highly oriented boron nitride composite material |
| CN105393318A (en) * | 2013-07-08 | 2016-03-09 | 原子能和替代能源委员会 | Annular sintered magnet with radial magnetization and reinforced mechanical strength |
| CN106373688A (en) * | 2016-08-31 | 2017-02-01 | 浙江东阳东磁稀土有限公司 | Method for preparing rare earth permanent magnet material |
| CN110444360A (en) * | 2019-07-19 | 2019-11-12 | 宁波可可磁业股份有限公司 | A kind of neodymium iron boron magnetic body and preparation method thereof |
| CN111276309A (en) * | 2018-12-04 | 2020-06-12 | 董元 | Method for preparing rare earth permanent magnet through hot press molding |
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2020
- 2020-07-10 CN CN202010663484.3A patent/CN111785504A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105393318A (en) * | 2013-07-08 | 2016-03-09 | 原子能和替代能源委员会 | Annular sintered magnet with radial magnetization and reinforced mechanical strength |
| CN104892004A (en) * | 2015-05-18 | 2015-09-09 | 山东理工大学 | Preparation process of highly oriented boron nitride composite material |
| CN106373688A (en) * | 2016-08-31 | 2017-02-01 | 浙江东阳东磁稀土有限公司 | Method for preparing rare earth permanent magnet material |
| CN111276309A (en) * | 2018-12-04 | 2020-06-12 | 董元 | Method for preparing rare earth permanent magnet through hot press molding |
| CN110444360A (en) * | 2019-07-19 | 2019-11-12 | 宁波可可磁业股份有限公司 | A kind of neodymium iron boron magnetic body and preparation method thereof |
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